In view of the importance of respiratory infections on COPD exacerbations, and of the gained knowledge of Haptoglobin subtypes on propensity to infection, we propose to investigate whether Haptoglobin subtypes are in correlation with the "frequent exacerbator" phenotype of COPD. We postulate that, since people with Hp 1-1 are more prone to infection, the frequency of the Hp 1-1 phenotype will be higher in "frequent exacerbators" of COPD than in "non- exacerbators".